The present invention relates to improved electrical commutators for large d.c. motors which typically have an output of greater than 500 horsepower. More particularly, it relates to novel composite commutator bars which have improved resistance to interface delamination and provide economic advantages.
Heretofore, electrical devices such as commutators were made from solid copper. In large d.c. motors there are a plurality of spaced commutator bars which may be one to two feet long. Thus the amounts of copper used in the complete commutator is considerable and becomes quite costly. Accordingly, it has been proposed to reduce the copper content by substituting duplex commutator bars made by bonding a copper strip to a steel stock. Such duplex bars were made by a number of techniques, such as pressed and sintered powders, electron beam welding and brazing. However, the specific process by which the copper is bonded to the steel does not overcome the fundamental problem with the duplex bar construction, which is that of high interface shear stresses resulting from differential thermal expansion of the two metals as temperature changes occur during motor operation. This causes delamination of the duplex bar and rapid failure of the commutator.